The invention process is concerned with the enhanced recovery of oil from underground formations. More particularly, the invention relates to a sequenced process for recovering hydrocarbons employing modified inverted 5-spot patterns containing horizontal and vertical wells.
Horizontal wells have been investigated and tested for oil recovery for quite some time. They have been proved economically successful to recover petroleum from many types of formation such as formations with highly viscous crude, thin pay zones, and difficult injectivity. It seems likely that horizontal wells will soon become more widely used in a variety of formations, especially for highly viscous oils and sands which cannot be efficiently or economically produced by conventional methods.
Various proposals have been set forth for petroleum recovery with horizontal well schemes. Most have involved steam injection or in situ combustion with horizontal wells serving as both injection wells and producing wells. Steam and combustion processes have been employed to heat viscous formations to lower the viscosity of the petroleum as well as to provide the driving force to push the hydrocarbons toward a well.
U.S. Pat. No. 4,637,461 discloses the use of inverted 9-spot and inverted 13-spot patterns having horizontal wells located along the borders of the well patterns between vertical wells. U.S. Pat. No. 4,646,824 shows numerous variations of modified inverted 5-spot well patterns having horizontal wells located along the borders between vertical wells. However, every well pattern disclosed in this patent teaches that all five vertical wells are injection wells.
Variations on inverted 5-spot and 9-spot well patterns with and without vertical corner wells are disclosed in U.S. Pat. No. 4,702,314. All horizontal wells in this reference are radial and located between the central injection well and corner production wells.
Additional variations on modified inverted 5-spot, 9-spot, and 13-spot well patterns are disclosed in U.S. Pat. No. 4,718,485, wherein all horizontal wells are placed on the borders of the well patterns. Some of the well patterns disclosed have additional interior injection wells. U.S. Pat. No. 4,727,937 discloses similar variations on modified inverted 13-spot patterns having horizontal wells located on the borders of the pattern; some patterns without vertical side wells and some patterns without vertical corner wells.